Prior art magnet arrangements of this species have at least one sensor which serves to determine the distance from a magnet pole surface to a conductive reaction rail for the magnetic levitation vehicle and to control the magnitude of the gap between the magnet pole surface and the reaction rail (e.g. DE 35 16 036 C2, EP 0 753 718 B1 (an corresponding U.S. Pat. No. 5,764,050).
The reaction rail, for example, is a longstator comprised of a plurality of stator packets arranged one behind the other and being part of a longstator linear motor for the magnetic levitation vehicle. Sensors for such magnet arrangements generally comprise one sensor head provided with at least one measuring and/or sensor coil and an electronic module which is assigned to the sensor head and which contains switching circuits, for example, that serve to generate, process and/or evaluate sensor signals and which is connected to a usual control circuit with a control element and a magnet current actuator in order to maintain the magnitude of the gap between the magnet pole face and the reaction rail to a pre-selected design value of 10 mm, for example.
The sensor heads of the sensors described are always next to a selected magnet pole and so arranged that they border at the same plane as its magnet pole face. In practice, the sensor heads with the assigned electronic modules form one L-shaped structural unit, with the sensor head being arranged in a space next to the magnet pole kept free from its magnet coil, and wherein the electronic module comes to rest at the front side of the magnet arrangement facing the guideway (e.g. DE 2004 012 748 A1 or ZEVrail Glasers Annalen, October 2003, special edition “Transrapid” P. 62, 63). Though a sensor of this layout and arrangement works faultless, it does not meet all the desired requirements.
For example, it is deemed disadvantageous that the sensor together with the assigned magnet pole moves during the operation of a magnetic levitation vehicle and that is therefore exposed to high mechanical loads. These loads might take an adverse effect on the electronic module and on the control of the gap. Though in most cases there are two sensors of this kind for reasons of redundancy, but a failure of electronic components should be avoided, if possible, because a safe control of the gap size constitutes an indispensable prerequisite for the levitation status and thus for the operation of a magnetic levitation vehicle.
Another disadvantage of prior art magnet arrangements results from the fact that the surface of the sensor head should be arranged exactly flush to the magnet pole face whose gap versus the reaction rail is monitored. This calls for a sophisticated fastening technique and therefore, apart from leading to an increase in the number of components, it also leads to a reduction in the failsafe operation of the sensor.